﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.IO;

namespace V5_EaspLibs.Core {
    public class DownFileHelper {
        private static readonly DownFileHelper m_Instance = new DownFileHelper();
        /// <summary>
        /// </summary>
        public static DownFileHelper Instance {
            get { return m_Instance; }
        }
        //TransmitFile实现下载
        public void DownFileTransmitFile() {
            HttpContext.Current.Response.ContentType = "application/x-zip-compressed";
            HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=z.zip");
            string filename = HttpContext.Current.Server.MapPath("DownLoad/z.zip");
            HttpContext.Current.Response.TransmitFile(filename);
        }

        //WriteFile实现下载
        public void DownFileWriteFile() {
            string fileName = "asd.txt";//客户端保存的文件名
            string filePath = HttpContext.Current.Server.MapPath("DownLoad/aaa.txt");//路径

            FileInfo fileInfo = new FileInfo(filePath);
            HttpContext.Current.Response.Clear();
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.ClearHeaders();
            HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);
            HttpContext.Current.Response.AddHeader("Content-Length", fileInfo.Length.ToString());
            HttpContext.Current.Response.AddHeader("Content-Transfer-Encoding", "binary");
            HttpContext.Current.Response.ContentType = "application/octet-stream";
            HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
            HttpContext.Current.Response.WriteFile(fileInfo.FullName);
            HttpContext.Current.Response.Flush();
            HttpContext.Current.Response.End();
        }

        //WriteFile分块下载
        public void DownFileWriteFileBlock() {
            string fileName = "aaa.txt";//客户端保存的文件名
            string filePath = HttpContext.Current.Server.MapPath("DownLoad/aaa.txt");//路径

            System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);

            if (fileInfo.Exists == true) {
                const long ChunkSize = 102400;//100K 每次读取文件，只读取100K，这样可以缓解服务器的压力
                byte[] buffer = new byte[ChunkSize];

                HttpContext.Current.Response.Clear();
                System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);
                long dataLengthToRead = iStream.Length;//获取下载的文件总大小
                HttpContext.Current.Response.ContentType = "application/octet-stream";
                HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));
                while (dataLengthToRead > 0 && HttpContext.Current.Response.IsClientConnected) {
                    int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小
                    HttpContext.Current.Response.OutputStream.Write(buffer, 0, lengthRead);
                    HttpContext.Current.Response.Flush();
                    dataLengthToRead = dataLengthToRead - lengthRead;
                }
                HttpContext.Current.Response.Close();
            }
        }

        //流方式下载
        public void DownFileFileStream() {
            string fileName = "aaa.txt";//客户端保存的文件名
            string filePath = HttpContext.Current.Server.MapPath("DownLoad/aaa.txt");//路径
            //以字符流的形式下载文件
            FileStream fs = new FileStream(filePath, FileMode.Open);
            byte[] bytes = new byte[(int)fs.Length];
            fs.Read(bytes, 0, bytes.Length);
            fs.Close();
            HttpContext.Current.Response.ContentType = "application/octet-stream";
            //通知浏览器下载文件而不是打开
            HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;  filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
            HttpContext.Current.Response.BinaryWrite(bytes);
            HttpContext.Current.Response.Flush();
            HttpContext.Current.Response.End();
        }
    }
}
